Good news :). After 13 years the database is more than a bit cranky... :)

Ah, sorry. I [b]removed[/b] my existing password from the "Password" box and then it worked.

At "User Control Panel → Profile → Edit account settings" I tried to change my email address but not my password.
1. Edit the "Email address" field.
2. The "Confirm email address" field contains my login name. Replace it by my new email address.
3. Enter my existing password in the "Current password" field ("To change your password, [b]your email address,[/b] or your username, you must enter your current password.")
4. Hit [ Submit ]
— [b][color=red]Error: You did not confirm your password.[/color][/b]
5. Enter my existing password in the "Confirm password" field (and reenter my new email address in the "Confirm email address" field)
— [b][color=red]Error: Your new password is the same as your existing password.[/color][/b]